Wine grapes consist of shells containing the pulp. When agitated in a fermentation tank, grape mash is formed consisting of the liquid components, i.e. the grape juice and the solid components, namely the shells, the pips and the rapes. Red wine grape mash is agitated to wash the red color, being mostly contained in the shells, out of the shells. The solid components enumerated above are also referred to as pomace.
Before fermentation and especially during the discharge of juice, the pomace of the grape mash tends to settle in the funnel-shaped bottom. To allow the pomace to be removed from the tank after the juice has flowed off, known tanks have a discharge screw provided at the lower end of the funnel-shaped bottom. Although all the pomace which enters the area of the screw is discharged by means of the screw, it happens often, especially when the pomace is not discharged immediately after the juice has been drained off, that the pomace cakes together to form a bridge above the screw and to prevent any further pomace from entering the area of the screw. Accordingly, it is often necessary in known tanks of this type to introduce a long rod through the filling orifice with the aid of which to destroy the bridge of pomace cake formed above the discharge screw and to poke additional pomace into the area of the screw.
In the known upright red wine fermentation tanks of the type described before, which have a substantially upright cylindrical shape, the agitators are arranged coaxially to the cylinder axis so that the agitator axis coincides with the center plane of the cylinder and the agitating members extend in the form of agitator arms or blades radially from the vertical agitator shaft.
Upright grape mash tanks of the type described before are used in cellarage for storing and/or treating white grape mash or red grape mash. While in the case of white grape mash the main function is to be seen in the storing and dripping of the grape mash, i.e. the separation of liquid and solid components, the treating function is an important additional element in the case of red grape mash, because contrary to white grape mash, red grape mash must be stirred during fermentation to wash out the red color from the shells.
However, regardless of the type of mash in the tank, there always exists the before-mentioned necessity to separate the solid and liquid components with the aid of so-called dripping means, usually a screen arrangement.
Although these known fermentation tanks operate normally in a satisfactory manner, it has been found that markedly inconsistent results are obtained with certain vine species, in particular for high-quality wines. This is probably due to the fact that tanks of specific dimensions, especially of particular height/diameter ratios, are better suited for certain vine species than others. The reason for this phenomenon is probably to be seen in functional differences of the agitator, which is of course adapted to the dimensions of the tank, so that different wine qualities are obtained for different high-quality vine species.
Further, it must be taken into consideration that red grapes cultivated in northern areas have a lesser content of red color than grapes grown, for example, in the Mediterranean region. In the case of the first-mentioned grapes grown for instance in Central European or North American regions it is, therefore, necessary to ensure a particularly thorough color extraction during treatment of the red grape mash in the fermentation tank.
Quite satisfactory results have been obtained, as regards a consistent and at the same time high wine quality on the one hand and the best possible color extraction on the other hand, with horizontal red grape fermentation tanks which are themselves of a horizontal cylindrical design and in which the agitator rotates about a horizontal shaft. But due to the unfavorable static conditions, such horizontal red grape fermentation tanks are much more difficult to control and, thus, much more expensive to produce.
Now, it is the object of the present invention to improve a fermentation tank of the type described before so that without affecting the high quality of the wines, a consistent high quality can be achieved even for different vine species, that perfect color extraction is rendered possible and that, finally, these advantages need not be paid for by unproportionately high production costs of the tank.